STUK-A112 . OCTOBER 1993

Gamma-emitting radionuclides in the bottom sediments of some Finnish

E. Uus, M. Puhakainen, R. Saxen STUK-A112 OCTOBER 1993

Gamma-emitting radionuclides in the bottom sediments of some Finnish lakes

E. Hus, M. Puhakainen, R. Saxen

FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY P.O. Box 268, SF-00101 HELSINKI Tel. +358 0 70821 ISBN 951-47-7932-0 ISSN 0781-1705

Painatuskeskus Oy Helsinki 1993 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

JLUS E, PUHs\KAlNEN M, SAXEN R. Gamma-emitting radionuclides in the bottom sediments of some Finnish lakes. STUK-A112, Helsinki 1993, 45 pp.

ISBN 951-47-7932-0 ISSN 0781-1705

Key words Chernobyl fallout, sediments, lake water, radionuclides

ABSTRACT

In 1988 and 1990 bottom sediment and surface water samples were taken from eight large lakes representing all five categories of deposition regions contaminated by the Chernobyl fallout in Finland. All samples were analysed for gamma-emitting radionuclides.

The 137Cs concentrations in surface waters varied in 1988 from 20 to 310 Bq m"3 and in 1990 from 78 to 170 Bq m'3. The other radionuclides of Chernobyl origin detected in water samples were 106Ru, 125Sb and 134Cs. In the sediments the total amount of 137Cs per square metre varied in 1988 from 1100 to 160 000 Bq m~2 and in 1990 from 14 000 to 250 000 Bq nT2. The maximum values were in Lake Pyhäjärvi. The maximum concentration of 137Cs in the surface layer of sediment (0-2 cm) was 55 700 Bq kg"1 dry wt in Lake Näsijärvi. In addition to the cesium isotopes 137Cs and 134Cs, Chernobyl derived 106Ru, 125Sb and 144Ce were detected in the surface layer of sediments in most of the lakes. ^Mn, '"Co and 110mAg were also detected in some lakes situated in the regions most contaminated by the Chernobyl fallout.

In 1988 the maximum concentrations of 137Cs and 134Cs were in the uppermost layer of sediment (0-2 cm) at almost all stations. In 1990, the cesium peaks already occurred at many stations in the second slice (2-5 cm), which may indicate downward diffusion of cesium in sediments or mixing of sediment layers during sampling. The most important factors affecting cesium values in sediments were the local amount of deposition and the type of sediment. This study did not reveal any correlation between the maximum depth of the lake and the area of the lake with the cesium amounts in the sediments.

3 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

CONTENTS Page

ABSTRACT 3

CONTENTS 4

1 INTRODUCTION 5

2 MATERIAL AND METHODS 6

3 DESCRIPTION OF THE LAKES 8

4 RESULTS 10

5 DISCUSSION 12

ACKNOWLEDGEMENTS 16

REFERENCES 17

FIGURES 20

TABLES 29

4 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

1 INTRODUCTION

In spring 1986, large areas of central and southern Finland were contaminated by radioactive fallout from the reactor accident at the Chernobyl NPP. During the initial deposition most of the lakes were coverei with ice. After melting of the ice in early May, the decisive factor affecting activity concentrations in the waters of Finnish lakes was the direct radioactive fallout deposited on the lake surface. Over a longer period of time, differences in the water quality of the lakes and the character of the drainage areas changed the activity concentrations in lake waters to some extent.

Apart from direct deposit on the surface of a body of water, radioactive substances entered lake systems as runoff from the surrounding drainage areas. The volume of runoff depends on many factors, for instance the type of soil in the drainage area. The most significant radionuclides in the Chernobyl fallout were the cesium isotopes 137Cs and 134Cs. Once in contact with soil, cesium is strongly adsorbed by the fine soil particles, which are carried by erosion and runoff from the drainage areas to bodies of water. The volume transported is greater when the drainage area has a grass-crop cover than when it is covered by forest.1819

In lakes many radionuclides are readily adsorbed by suspended particles and presumably settle on the bottom. The total amount of radionuclides in the sediment depends on many biological and geochemical processes in the aquatic environment such as particle production, sedimentation rate, resuspension, etc.

The adsorption of cesium by sediments is mainly determined by the presence of clay minerals, and the adsorption ratio at low salinity is found to be roughly proportional to the clay content in the sediment. Ion exchange on the clay minerals is the prevailing adsorption mechanism for cesium.9 Most of the 137Cs occupies highly selective exchange sites on the clay fraction in the sediment. It is therefore unlikely that any large fraction of the 137Cs would move from the bottom except through erosion of the sediment.10 Once settled on the bottom, cesium generally remains in the sediment.

The fate of 137Cs and ^r originating from nuclear weapons tests has been monitored in Finland since the mid-sixties. The amounts of radionuclides in the bottom sediments of some large Finnish lakes were studied in the late 1960s and late 1970s.4 In 1988 and 1990 most of the sediment and water samples were taken from the same stations.

5 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

2 MATERIAL AND METHODS

In 1988 and 1990 bottom sediment and surface water samples were taken from the Lakes Ontojärvi, Pielinen, Kallavesi, Konnevesi, Päijänne, Keurusselkä, Näsijärvi and Pyhäjärvi (Fig. 1). The lakes represent all the five categories of deposition regions contaminated by the Chernobyl fallout in Finland (Fig. 2)1 and they are part of four large watercourses discharging into the .

The locations of the sampling stations in the eight lakes are shown in Figs 3 and 4. In general, the deepest sedimentation basins were chosen as sampling sites. However, because sampling from bottoms deeper than 40m caused difficulties with our small boat and heavy sediment corers, this principle was given up in some cases. For example, station 6 on Päijänne does not represent the deepest basin of Ristiselkä, but another smaller basin with a soft bottom.

The samples were taken from a 5m boat with an outboard motor. As no winch was available, the cores were raised by hand. The boat was anchored during the sampling, which normally took 1-2 hours per station. Especially in 1990 the weather was quite windy during sampling, which probably had an effect on the quality of samples.

In 1988 the sediment samples were taken by a STUK corer, consisting of a stainless steel body and an inner plexiglass tube with an inner diameter of 64 mm, and with a sectioning apparatus for 2 and 5 cm thick slices (Fig. 5). Six parallel samples were taken at each station and the uppermost layers were sectioned into 2 cm thick subsamplcs, then 3 cm and 5 cm subsamples using plastic slides (Fig. 5). The corer is 50 cm long and weighs 12.5 kg. Because the sediment was very soft in most of the lakes, the corer tended to penetrate too deep into the sediment. At many stations it was therefore held up with the rope during the relieving of the closing valve with a messenger weight. In general, however, the samples taken by the STUK corcr had an undisturbed sediment surface and clear water above it, and satisfied our quality requirements.

In 1990 the samples were taken by a Limnos sampler manufactured and patented by Limnos Oy, Turku Finland (Fig. 5). The sampler consists of a polycarbonate tube with an inner diameter of 94 mm and a closing valve and skeleton of stainless steel. The total length of the sampler is 94 cm and the weight 4 kg, but it can be equipped with 2-6 extra lead weights of 1.85 kg each. The special feature of the sampler is that the tube consists of a series of equal 1-cm-high

6 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY rings placed one on top of one another. The rings rotate round a shaft so that they cut the sediment profile in 1-cm-thick slices on an auxiliary plate (Fig. 5). Normally we used 2-4 lead weights in sampling and took 2 parallel samples at each station. The samples were sliced immediately in the boat. They were generally in good condition when they arrived on the surface. Slicing in the rocking boat, however, was difficult as the weather was quite rough at many stations during the sampling.

The parallel subsamples were combined for analyses. After each slicing the sectioning apparatus was washed with a wash bottle and the water added to the sediment sample. Distilled water was used for washing in 1988 and local lake water in 1990. The samples were frozen and stored in plastic bags before analysis. Sediment samples were freeze-dried before dry weight determination. Ignition loss was determined from the weight loss of dried sediment after ignition at 550 °C for 3-3,5 hours.22 Organic carbon was determined from sediments using dicromate- ferroammoniumsulphate titration method.3

The surface water samples were taken at the same stations as the sediments. The volumes of the water samples were 30 1. The samples were concentrated by evaporation.

All the samples were analysed for gamma-emitting radionuclides. A cylindrical geometry (volume 30 ml) was used both for dried sediment samples and for concentrated water samples. Aliquots of about 30 g of dried sediment and evaporation residues of 30 1 of lake water were analysed. Gammaspectrometric analyses were performed using either lithium-drifted or high purity germanium detectors with relative efficiencies between 30% and 39%. The measuring times varied between 60 and 1000 minutes. The activity concentrations of the samples were calculated using the computer program GAMMA-83.20-21

7 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

3 DESCRIPTION OF THE LAKES

Ontojärvi Lake Ontojärvi (Fig.4) is located in the easternmost part of the drainage basin. It is a regulated lake. The surface area of the Ontojärvi-Lentua subbasin is 4730 km2 and the lake percentage is 11.9 %. There are 1174 lakes in the area. The surface area of Lake Ontojärvi is 95 km2. Water entering the lake from the rivers is rich in humic substances. There are no industrial or other noteworthy effluents in the lake.17

Pielinen Lake Pielinen (Fig.4) is the central lake of the northeastern part of the Vuoksi watercourse. The surface area of Lake Pielinen is 867 km2. The mean depth of the lake is 9.9 m and the maximum depth 60 m. The volume of the lake basin is 8.5 km3, and the water retention time 670 d with a mean outflow of 147 m3/s. The shores of Lake Pielinen are mainly characterized by clay and silt; account for 10 - 20%. The water of Lake Pielinen is almost entirely natural and oligotrophic. Especially in the northern part of the lake the colour of the water is medium brown and the open waters are oligohumous and oligotrophic.12 The towns of and load Lake Pielinen and the areas close to the towns are slightly eutrophicated.

Kallavesi Lake Kallavesi (Fig.4) is the central lake of the Kallavesi basin. Humic substances arc characteristic of water in the lake. The surface area of the lake is 425 km2 and the mean outflow 111 m3/s. The length of the lake is 90 km and the maximum width 15 km. In the northern part of the lake, the impact of settlement in the town of Kuopio and of industrial effluents is evident. During the stratification periods the amount of oxygen in the near-bottom water is low, and turbidity caused by plankton algae occurs in the area close to the town.14

Konnevesi The area of Lake Konnevesi (Fig.4) is 187 km2 and the mean depth 9.8 m. The lake is part of the Rautalampi basin, the drainage area of which is 5765 km2 and the lake percentage 20.9%. The mean outflow is 48 m3/s and the theoretical re­ tention time of the lake is 442 days. In the upper courses of the Rautalampi water system there arc large peat bogs. Humic substances are therefore characteristic of the waters. The colour values in the large lakes of the upper courses of the basin are 50 mg Pt/1. Humic substances decompose and settle as they come downstream. The colour of the water in Lake Konnevesi is therefore only about 20 mg Pt/1.13 During the last decades the southern part of the lake has been slightly eutro-

8 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

phicated, which is indicated by decreased concentrations of oxygen in hypo- limnion.

Päijänne Lake Päijänne (Fig.3) is the central lake of the Kymijoki drainage basin. The mean depth of Lake Päijänne is 17 m. The deepest sites are located at Ristiselkä, Souselkä, Tehinselkä and in the southeastern part of Asikkalanselka. The deepest site of all the Finnish lakes, 95 m, is located near the eastern shore of Ristiselkä. The surface area of Lake Päijänne is 1100 km2. The maximum length is 120 km and maximum width about 28 km. The mean annual precipitation of the area is 650-700 mm, evaporation about 400-500 mm and runoff 150-250 mm.The mean inflow of the main stream to Lake Päijänne is 139 m3/s and the mean outflow 209 m3/s. The lake is covered by ice for an average of 4.5 months a year. The theoretical retention time for the whole lake is about 2.7 a.

Fields account for some 13% of the immediate drainage area of Asikkalanselka. Fields in the immediate drainage area of central Päijänne account for 10% and bogs are few in number. In the immediate drainage area of Ristiselkä fields account for 7% and are usually located near the shore.

A considerable load of effluents is focused in the northern and central parts of the lake. In some polluted areas the near-bottom water is often without oxygen during winter and the contents of nutrients are high. Souselkä can be regarded as slightly eutrophicated. Tehinselkä and Asikkalanselka are oligotrophic and the water is of good quality.815

Keurusselkä. Näsijärvi. Pyhäjärvi The Lakes Keurusselkä, Näsijärvi and Pyhäjärvi (Fig.3) are part of the drainage basin of the River Kokemäenjoki, which is the fourth largest drainage basin in Finland. The lake percentage in the area is 10%, which is the mean value for the whole country. The surface areas of Lakes Keurusselkä, Näsijärvi, and Pyhäjärvi are 119 km2, 257 km2 and 124 km2, respectively. The mean depths of the lakes are 6.4 m, 14 m and 5.6 m.

Humic substances and local weaken the water quality of the northern parts of Lake Keurusselkä. The central part of the lake is nearly in natural condition. Settlement in the town of Mänttä has a slight impact on the waters of the southern part of the lake.

In the northern parts of Näsijärvi the quality of the water is near natural. The values for lignine refer to the load on upper parts of the watercourse. The southern part of Näsinselkä is heavily polluted by effluents from the forest industry.

9 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

Water exhange is rapid, and mixing is effective in the northern parts of Lake Pyhäjärvi. Therefore, the heavy loading caused by settlement in the city of Tampere and by various industries, has not completely spoiled the lake. In spite of cleaning operations, the northern part of the lake is still highly eutrophicated.16

4 RESULTS

The concentrations of radionuclides in the surface water of the eight lakes are given in Table I. The 137Cs concentrations in the water samples studied varied in 1988 from 20 to 310 and in 1990 from 78 to 170 Bq m3. The decrease in "7Cs activity during the two years was 50 - 60%. The other radionuclides of Chernobyl origin detected in the water samples were 106Ru, 12SSb and 134Cs.

Tables II and III show some characteristics of the sediment samples taken in 1988 and 1990. In most of the sediments the organic C contents were 4 to 9% of the dry matter. In sediment from Lakes Pielinen and Päijänne the organic C contents were lower, 2 - 3%.

The concentrations of radionuclides in the sediment samples are presented in Tables IV and V. The impact of the Chernobyl fallout was clearly visible in the uppermost layers of the bottom sediment. In addition to the cesium isotopes ,37Cs and 134Cs, Chernobyl-derived 106Ru, 125Sb and 144Ce were detected in the surface sediments in most of the lakes. 54Mn, ^Co and 1IOmAg were also detected in some lakes situated in the regions most contaminated by the Chernobyl fallout.

In 1988 the maximum concentration of 137Cs was in the topmost sediment layer (0-2 cm) at all sampling stations. However, the highest amounts per square metre were in some lakes (Pielinen, Kallavesi and Konnevesi) in the 2-5 cm layer (Figs 6 and 7). The sediment of Konnevesi was very loose and the activity was mixed equally into the three uppermost layers. Lake Pielinen is located in the area with low Chernobyl fallout and the maximum caused by the fallout of 1960s is now in the 2-5 cm layer. The highest concentration of 137Cs in the surface layer of sediment, 55 700 Bq kg"1 dry wt, was found at station 11 in Näsijärvi.

In 1990 the maximum concentration was in Pyhäjärvi, Keurusselkä and Ontojärvi in a deeper sediment layer (2-5 cm) than in 1988. In the other lakes (Päijänne, Näsijärvi and Konnevesi) the maximum concentration of 137C was still in the top­ most layer. At station 11 in Näsijärvi the maximum concentration was a little lower than in 1988, i.e. 48 600 Bq kg"1 dry wt.

10 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table VI presents the total amounts of 137Cs in sediments of the lakes in different years and the the total deposition values due to Chernobyl fallout in the same areas on October 1, 1987 (the average municipal deposition values have been used). The total amount of 137Cs per square metre in bottom sediments at the sta­ tions studied varied in 1969 from 1400 to 10 000 Bq nr2and in 1978 from 1000 to 13 000 Bq m~2. In 1988 the corresponding ranges were from 1100 to 160 000 Bq m"2and in 1990 from 14 000 to 250 000 Bq m~2. The maximum value was re­ corded in Pyhäjärvi each year. The 137Cs profiles in the cores (in Bq m"2) are shown in Figs 6-9.

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5 DISCUSSION

The scattered distribution of deposition on the earth was one of the most characteristic features of the Chernobyl fallout. The presence of radioactive substances in lake basins was partly caused by direct deposition on lake surfaces and partly by transport from the surrounding drainage area. The total amounts of deposited radionuclides varied from area to area. In addition, there seemed to be considerable variation in the comparative ratios of different nuclides.

According to the country-wide fallout survey made in Finland,1 the highest average municipal deposition of 137Cs in the lake basins studied was 64 kBq m"2 in Vuolleselkä in the Lake Keurusselkä. Likewise, the highest 137Cs concentrations in water were in Keurusselkä in both 1988 and 1990: 310 and 170 Bq m"3. The lowest deposition value was only 2.2 kBq m~2 in the area of Lake Pielinen, which was also reflected as a low 137Cs content in water. In general, the 137Cs concentrations in w,.ter conformed closely to the local deposition values, except at Ristiselkä in Lake Päijänne, in Lake Konnevesi, and in particular in Lake Ontojärvi, where the concentrations in water were relatively high compared with the local deposition values. At least in the case of Ontojärvi, this could be associated with the high content of humic substances in water. A considerable part of the cesium there may be in colloid form and remains in the water. Between 1988 and 1990 the water/ deposition ratio decreased in all the lakes, indicating sinking of the cesium into sediments.

The water/sediment ratio of 137Cs was highest in Lake Konnevesi in 1988. The high ratio might indicate some tailurc in the sampling of sediments because the radionuclide concentrations in the surface sediment layers were very low. However, the samples taken from Konnevesi in 1988 looked very good, with an undisturbed surface layer and a clear water layer above it. Therefore the low values could also be due to the patchiness of the radionuclides in sediments mentioned by many authors.711 The ratio was smallest in Pyhäjärvi, which could indicate rapid sedimentation of cesium in this lake. In 1990 the ratios were closer to each other than in 1988, the highest value being in Ontojärvi, probably because the cesium remained in colloid form in the water, as stated before.

Tiie comparability of the total amounts of 137Cs in sediments (Bq m~2) and the local deposition values was less unique than that of water and deposition. This may be affected by the type of sediments. For example, deposition was virtually same in the southern part of Lake Näsijärvi and in Lake Pyhäjärvi. However, the 137Cs concentrations (Bq kg"1 dry wt) in the surface sediment were higher in

12 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Näsijärvi, but the total amounts per square metre were clearly higher in Lake Pyhäjärvi. Moreover, in our previous investigations in 1969 and 1978, the highest total amounts of 137Cs were detected in the sediments of Lake Pyhäjärvi (the sampling place was the same). The lake is heavily loaded by industrial effluents and sewage from the city of Tampere. The type of bottom at the sampling station is sulphidic "gyttjaclay", but the thickness of this soft sediment layer is only about 15 centimetres, which indicates that sedimentation is not permanent or that it should be very slow. The thin layer of soft sediment can be explained by the "river-like" character of Lake Pyhäjärvi. Due to near-bottom currents the sediment in Lake Pyhäjärvi is more compact than in Lake Näsijärvi, where the surface sediment layer is very loose. Thus the total amount of 137Cs is higher in sediments where the amount of recently settled clay particles per square metre is higher and the water content of the sediment is lower.

The difference between the amounts of radiocesium in sediments and the local deposition values was more conspicuous in 1988 than in 1990. In 1988, the sediment/deposition ratio varied considerably and only in Lakes Pyhäjärvi, Näsijärvi, Ontojärvi (Merjanselkä) and Pielinen were the amounts of 137Cs in the sediments higher than in the deposition. In 1990, the total amounts of 137Cs in the sediments of almost all lakes were almost twice as high ai die corresponding average municipal deposition values. Compared with the total amounts of 537Cs at the same stations in the late 1960s and 1970s, the values were now about 70-fold at their highest in Asikkalanselkä and about fivefold at their lowest in Lake Ontojärvi.

According to our results, the main factors affecting 137Cs values in sediments were the local amount of deposition and the type of sediment. Särkkä et ai.23 stated that the maximum depth of the lake, the area of the lake, retention time and the amount of precipitation one week after the Chernobyl accident were associated with increased amounts of cesium in the sediments of some lakes in Central Finland. Our material does not reveal any correlation between the maximum depth of the lake and the area of the lake with respect to cesium amounts in the sediments. However, almost all of the lakes studied could be classified as "large lakes".

Kansanen et ai.7 stated that the content of radionuclides showed considerable spatial variation on the lake bottom in southern Lake Päijänne, and that there was a clear tendency for concentrations to increase with depth as a result of the focusing effect. Likewise, the results of Meili et al.11 showed considerable areal variation in some Swedish lakes. Our material does not permit this kind of exam­ ination, because we had to limit our sampling to 1 or 2 stations in every lake. The

13 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

spatial variation of radionuclide concentrations could, however, explain some of our unexpected low values.

If we compare the total amount* of cc«'i:;n in Finnish lake sediments with those reported from the coastal areas of Finland and from the open Baltic Sea, the maximum values found in some lake sediments seem to be higher. In 1990, the maximum value for 137Cs in the coastal areas of the was 80 kBq m"2 and in the open Gulf of Finland 40 kBq m"2.5,6

The vertical profiles of 137Cs given in Figs 6-9 show that in 1988 the maximum amount of cesium was in the uppermost sediment layer (0-2 cm) at almost all the stations. Some of the 137Cs found in the deeper layers is certainly the residue from fallout caused by nuclear weapon tests in the past. However, detection of J34Cs (which obviously originated from the Chernobyl fallout) in the deeper layers most probably indicates mixing of sediment layers. This disturbance of sediment layers can be due to the sampling device or methods, to bioturbation caused by benthic animals, or to "wandering" of radionuclides in sediments.

In 1990, the cesium peaks occurred at many stations in the second slice (2-5 cm), which also may indicate downwards diffusion of cesium in sediments because the real sedimentation rate in Finnish lakes has proved to be very low. In studying sediments from soft-water lakes in New England and Scandinavia, Davis et ai.2 noticed that the profiles of 137Cs had their maxima at the surface, but 137Cs also occurred in sediments at depths many decades older than the beginning of the 1?7Cs fallout. They argued that the occurrence of 137Cs at the prefallout sediment depths is due mostly to net downward molecular diffusion and adsorption. They also argued that the surface concentration is due to upward diffusion and adsorption, recycling of sedimentary I37Cs in the water column, and delayed input from the watershed. They stated that the mobility of 137Cs in the sediment may be a function of release by organic decomposition and the scarcity of clay minerals /or adsorption. In general, the sediments in Finnish lakes are very loose and rich in organic components. The mobility of cesium would therefore be easier in lake sediments than in sediments typical of Finnish coastal areas.

Apart from the cesium isotopes, Chernobyl-derived 106Ru, 125Sb and 144Ce were detected in the surface layer of sediments in most of the lakes, especially in 1988. ^Co was detected in 1988 in the surface sediments of Näsijärvi and Asikkalan- selkä and still in 1990 at station 11 on Näsijärvi. In these samples Chernobyl fallout may be the only potential source of cobalt. 54Mn was found only in one sediment sample taken from Näsijärvi in 1988.

14 FINNISH CENTRE FOR RADiATION STUK-AI 12 AND NUCLEAR SAFETY

In 1988, the 106Ru/ 134Cs and 144Ce/134Cs ratios were higher in the local deposition values than in lake sediments. In the Kuhmo region the share of 106Ru and 144Ce in deposition was higher than in other areas of Finland. This was also visible in the sediments of Lake Ontojärvi, which is situated in the Kuhmo region. The ratios of 106Ru and 144Ce to 134Cs in sediments were higher there than in the other lakes. The decay-conected ratios of 144Ce and 106Ru to 134Cs inaeased substantially between 1988 and 1990, which means that cerium and ruthenium transferred to sediments later than cesium. Between 1988 and 1990 125Sb seemed to migrate downwards from the surface layer of the sediment.

Sediments were taken with different sampling devices in 1988 and 1990. In 1990 the two sampling devices were compared at one station on Lake Ontojärvi. The results presented in Tables III and V and in Fig. 10 show that in general the differences between the two corers were small. Nevertheless, the Limnos sampler obtained - at least in this intercomparison - some 15% more 137Cs per square metre. This was caused by different amounts of dry matter in the samples. Owing to its smaller diameter, the STUK corer may have a somewhat higher "packing effect" on the uppermost loose sediment layer, because the dry weights obtained by the Limnos sampler from these layers were smaller. However, both devices proved to be useful in surveys of this kind. In rough weather the STUK corer was easier to handle in a small boat.

15 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-AI 12

ACKNOWLEDGEMENTS

We are indebted to Pertti Palanne, Tero Laiho and Mirja Rosenberg for assistance in sampling and to Esko Hyttinen, Ulla Koskelainen and Irja Putkonen for assisting in pre-treatment and analysis of the samples.

16 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

REFERENCES

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2. Davis R, Hess T, Norton S, Hanson D, Hoagland K, Anderson D. 137Cs and 210Pb dating of Sediment from soft-water Lakes in New England (U.S.A) and Scandinavia, a Failure of 137Cs dating. Chemical Geology 44:151-185, 1984.

3. Gaudette HE, Flight WR, Toner L and Folger DW. An inexpensive titration method for the determination of organic carbon in recent sediments. Journal of sedimentary petrology 44, 1, 249-253,1974.

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7. Kansanen PH, Jaakkola T, Kulmala S, Suutarinen R. Sedimentation and distribution of gamma-emitting radionuclides in bottom sediments of southern Lake Päijänne, Finland, after the Chernobyl accident. Hydrobiologia 222: 121-140,1991.

8. Lake Päijänne Symposium. Biological research reports from the university of Jyväskylä 10. University of Jyväskylä, Jyväskylä 1987.

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11. Meili M, Rudebeck A, Brewer A, Howard J. Cs-137 in Swedish Forest Lake Sediment, 2 and 3 Years after Chernobyl.The radioecology of natural and artificial radionuclides. Proceedings of the XVth Regional Congress of IRPA, Gotland, , 10-14 September,1989.

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13. Publications of the National Board of Waters 32, Kymijoen vesistön yläosan vesien käytön kokonaissuunnitelma (Integrated water resources development plan for the upper part of the Kymi River drainage basin). Vesihallitus- National Board of Waters, Finland, Helsinki 1980.

14. Publications of the National Board of Waters 34, Kallaveden reitin vesien käytön kokonaissuunnitelma (Integrated water resources development plan for the Kallavesi watercourse). Vesihallitus- National Board of Waters, Finland, Helsinki 1980.

15. Publications of the National Board of Waters 36, Päijänteen alueen vesien käytön kokonaissuunnitelma (Integrated water resources development plan for the lake Päijänne area). Vesihallitus- National Board of Waters, Finland, Helsinki 1981.

16. Publications of the National Board of Waters 38, Kokemäenjoenvesistön vesien käytön kokonaissuunnitelma (Integrated water resources development plan for the River Kokemäenjoki drainage basin). Vesihallitus-National Board of Waters, Finland, Helsinki 1983.

17. Publications of the National Board of Waters 49, Oulujoen, Ii- ja ­ joen sekä Kuusamon vesistöjen vesien käytön kokonaissuunnitelmat (Integrated water resources development plans for the Oulujoki, Iijoki and Kiiminkijoki river basins and watercourses). Vesihallitus-National Board of Waters, Finland, Helsinki 1986.

18. Ritchie JC, McHenry JR. Application of radioactive fallout cesium-137 for measuring soil erosion and sediment accumulation rates and patterns: A Review. J.Environ.Qual. 19: 215-233, 1990.

19. Ritchie JC. McHenry JR, Gill AC. Fallout 137Cs in the soils and sediment of three small watersheds. Ecology 55: 887-890,1974.

18 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

20. Sinkko K. Computer analysis of gamma-ray spectra in sample mea­ surements. Licenciate Thesis. Helsinki: University of Helsinki, Department of Physics, 1981. (In Finnish)

21. Sinkko K, Aaltonen H. Calculation of the true coincidence summing correction for different sample geometries in gamma-ray spectroscopy. Report STUK-B-VALO 40. Helsinki: Finnish Centre for Radiation and Nuclear Safety, Surveillance Department, 1985.

22. Standardi SFS 3008. Veden, lietteen ja sedimentin kuiva-aineen ja hehku- tusjäännöksen määritys. Helsinki, 1990.

23. Särkkä J, Luukko A, Horppila P, Jämsä A and Valtonen T. Chernobyl cesium fallout in the sediment and fish of lakes of different sizes in Finland. Verh.Internat.Verein.Limnol.24: 2346-2351, Stuttgart, 1991.

19 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

*

<ä O g g O

Fig. I. location of the lakes studied. A= Ontojärvi, B~ Pielinen, C- Kallavesi, D= Konnevesi, E= Päijänne, F= Keurusselkä, G- Näsijärvi, 11- Pyhäjärvi,

20 FINNISH L TNTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

t

V .

4 100 ka

Fig. 2. Division of Finnish municipalities into five regions according to average surface activities of ls7Cs caused by the Chernobyl fall-out on October 1, 1987.'

21 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

KEURUSSELKÄ PÄIJÄNNE

ICtURUO JYVÄSKYtA

,10

MÄNTTÄ

JAMSÄ

NÄSIJÄRVI

TAMPERE ffll ^^JV PYHÄJÄRVI

IAHTI

22 FINNISH CENTRE FOR RADIATION STUK-AU2 AND NUCLEAR SAFETY

ONTOJÄRVI PIELINEN

KUHMO KALLAVESI

KONNEVESI

Fig. 4. Location of the sampling stations in Lakes Ontojärvi, Pielinen, Kallavesi and Konnevesi (above).

Fig. 3. Location of the sampling stations in Lakes Päijänne, Keurusselkä, Näsijärvi and Pyhäjärvi (on the left).

23 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-Al 12

Fig. 5. Construction (A) of the STUK corer and its slicing device and (B) of the Limnos sampler with a built-in slicing system.

24 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

en o ro o o o o o O O o o o o o o o O o o o o o o o o o o o o o o o 0-2 Bq/m' 0-2 Bq/m 2-5 2-5 5-10 5-10 10-15 10-15 15-20 15-20 20-25 20-25 25-30 25-31/ 30-35 1988 30-35 1988

PIELINEN, SUURSELKK(3) KALLAVESI ,MUURAISSAAREK4)

K) r^ 0) CD O ro r- CD CO o O O o O o O O O o o O O o O o O o O o o O O o O o O o O o o O o o O o O o o o o 0-2 Bq/ nr 0-2 i Bq/m 2-5 2-5 5-10 5-10 10-15 10-15 15-20 15-20 20-25 20-25 25-30 25-30 30-35 30-35 1988 1988

PKIJKNNE ,RI ST ISELKK( 6) PKIJKNNE ,S0USELKK(1)

ro CO o ro en CO o O o o o o O o^ a o o O o o o o o o o o o O o o o o o o o o o o o o o o o o o o o Bq/ro2 0-2 Bq/m* 2-5 5-10 10-15 15-20 20-25 25-30

1988 1988

PKIJKNNE ,TEHINSELKK( 8) NHSIJKRVI ,SIILINKARI( 12)

Fi#. 5. Vertical distribution of ,37Cs (Bq m'2) in bottom sediments at stations 3, 4, 6, 7, 8 and 12 in 1988.

25 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

ro r^ at co o ro o o o o o o O o o o o o o o O o o o o o o o o o o o o o o o o o 0-.O Bq/m' 0-2 Bq/m -5 2-5 5--10 5-10 10--15 10-15 15--20 15-20 20- 25 20-25 25- 30 25-30

1988 1990

PKIJKNNE , ASIKKALAO)

M 00 o ro 0- 0) 00 o O o at o o CD o o o o o O o o o o o o o o o O o o o o o o o o o o o o o o o o o o o Bq/IT/ 0-2 Bq/m Il F* 2-5 s-io S 5-10 10-13 10-15 15-20 15-20 20-25 20-25 25-30 25-30

1988 1990

KEURUSSELKÄ, VU0LLESELKK(10)

f-. 01 00 o ro J^ rjl 00 o o o o o O o O o o o o o o o o O o o o o o o o o O o o o o O o o j-t wS/SS-&S--VjVS-ktWM!l^^ I Bq/m2 0-2 l Bq/m2 2-5 5-10 10-15 15-20 20-25 25-30 30-35 1988 1990

NÄSIJÄRVI, NKSISELKK(11)

Fl£. 7. Vertical distribution of wCs (Bg m'2) in bottom sediments at stations 1, 2 and 5 in 1988 and 1990.

26 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

en o ro r* CT) CO o o o o O O O O o o o o O o O O o o o o o O o O O o o o o o O o o • o 0-2 Bq/ m 0-2 Sq/nT 2-5 2-5 5-10 5-10 10-15 10-15 15-20 15-20 20-25 20-25 25-30 25-30

1988 1990

0NT0JKRVI ,MERJANSEl_KK(1)

ro f* CT) CD o ro «v (T) CD o O O O o o O o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o o 0-2 Bq/rrT Bq/nr 2-5 5-10 10-15 15-20 20-25 25-30 30-35 19S8 1990

ONT0JHRVI, MULKKUSAARET*2)

ro 1- CT) cc o ro CO 00 o O o O o o O o o o o O o O o o o o o o o O o O o o o o o o o o o O o o o o a o o 2 0-2 Bq f m2 0-2 1 Bq/m 2-5 2-5 5-10 5-10 10-15 10-15 15-20 15-20 20-25 20-25 25-30 25-30 30-35 1988 1990

KONNEVESI ,K0NNESELKK(5

Fig. 8. Vertical distribution of "7Cs (Bq m'2) in bottom sediments at stations 9, 10 and 11 in 1988 and 1990.

27 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

ff) o en o o o o o o o o o o o o o o o o o o o o o o o o o o 0-2 Bq/m' 2-5 5-10 10-U 1988

M i^ 0) 00 o ro «•v CT) O o o o o o o o O o o o o o o o a o o o o o o o o o o o o o o o o n-? te» ! 1 Bq/mF ' o-s SSgfä 5-10^^

1990

Fig. 9. Vertical distribution of 13Cs (Bq m'2) in bottom sediments at station 13 in 1988 and 1990.

Bq/m* Bq/m'

.!">;0S-C0RER STUK-C0RER

o a o a ö o o o o o o TTT1 Bq/kg ""I I I I I I I I Bq, kg

UMNOS-COREn STuK-CORER

F/£. 70. Vertical distribution of wCs (given both in Bq kg'1 and Bq m~2) in bottom sediments taken with two different corers at station 1 in 1990.

28 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table I. The concentrations of gamma-emitting radionuclides in surface water samples in 1988 and 1990.

Lake Sampling Bq m'3 Sampling station date 106Ru ,25Sb 134Cs 137Cs

Ontojärvi 2) Mulkkusaaret 2.8.88 01 0 42 160 ft 24.8.90 0 0 9.3 78

Pielinen 3) Suurselkä 3.8.88 0 0 4.0 20

Kallavesi 4) Muuraissaaret 4.8.88 12 0 9.4 35

Konnevesi 5) Konneselkä 4.8.88 0 8.1 80 270 » 22.8.90 0 0 23 150

Päijänne 6) Ristiselkä 7.9.88 0 8.4 46 170 9) Asikkalanselkä 6.9.88 9.8 12 83 290 fr 24.8.90 0 0 24 160

Keurusselkä 10) Vuolleselkä 13.7.88 0 0 86 310 ?! 3.8.90 0 0 26 170

Näsijärvi 11) Näsiselkä 8.9.88 19 11 81 280 H 23.8.90 0 4 23 160

Pyhäjärvi 13) Lehtisaari 9.9.88 11 9.8 68 240 n 23.8.90 0 0 25 160

below the detection limit

29 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

Table II. Ignition loss, content of organic carbon, ratio of dry weight to volume and visual description of the sediment samples in 1988.

Lake Layer dry wt. Ignition Org. Type volume loss C of sediment Sampling station cm gem"3 % %

Ontojärvi 1) Merjanselkä 0- 2 0.11 18.2 6.6 dark brown mud 12.3 m 2- 5 0.21 12.9 4.1 ft 5-10 0.18 13.7 4.7 it 10- 15 0.16 16.6 5.6 n 15 -20 0.14 19.4 6.5 ti 20-25 0.14 20.1 6.3 n 25 -30 0.15 19.2 6.5 n

Ontojärvi 2) Mulkkusaaret 0- 2 0.077 22.1 8.4 dark grey mud 24.4 m 2- 5 0.087 22.8 8.0 II 5-10 0.093 24.6 7.6 II 10- 15 0.089 26.3 8.0 II 15-20 0.090 28.3 9.2 II 20-25 0.091 30.1 9.4 II 25-30 0.095 30.7 9.4 II

Pielinen 3) Suurselkä 0- 2 0.14 10.9 3.1 reddish brown sludge 29.5 m 2- 5 0.23 9.4 2.3 watery sludge 5-10 0.29 7.4 2.2 dark clay 10- 15 0.30 8.5 2.4 grey clay 15-20 0.28 9.5 2.6 n 20-25 0.28 9.5 2.5 n 25 -30 0.31 8.2 2.3 n 30-35 0.32 7.9 2.5 brown clay

30 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table II. continued

Lake Layer dry wt. Ignition Org. Type volume loss C of sediment Sampling station cm gem'3 % %

Kallavesi 4) Muuraissaaret 0- 2 0.093 20.4 7.6 black sludge 32.2 m 2- 5 0.13 17.4 5.6 n 5-10 0.18 10.2 3.3 n 10- 15 0.18 10.2 2.8 watery grey mud 15-20 0.16 11.8 3.0 n 20-25 0.15 12.5 3.1 •1 25-30 0.14 15.6 4.1 n 30-35 0.14 16.2 4.3 ii

Konnevesi 5) Konneselkä 0- 2 0.072 21.7 5.8 watery mud 40.0 m 2- 5 0.087 21.7 5.8 n 5-10 0.076 23.0 6.2 B 10-15 0.077 24.2 6.7 II 15-20 0.071 25.4 6.7 II 20-25 0.075 25.6 6.1 II 25-30 0.074 25.9 7.1 II 30-35 0.080 24.5 7.6 II

Päijänne 6) Ristiselkä 0- 2 0.10 12.8 4.3 dusty mud 45.0 m 2- 5 0.14 13.9 4.7 mottled mud 5-10 0.22 8.2 2.8 muddy clay 10-15 0.42 4.3 0.9 grey clay 15-20 0.65 2.9 0.8 n 20-25 0.50 4.1 1.2 II 25-30 0.35 6.4 1.8 tough grey clay 30-35 0.31 7.9 2.0 ti

31 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

Table //. continued

Lake Layer dry wt. Ignition Org. Type volume loss C of sediment Sampling station cm gem"3 % %

Päijänne 7) Souselkä 0- 2 0.15 13.4 4.9 watery sludge 41.0 m 2- 5 0.21 9.1 2.9 watery black sludge 5-10 0.35 5.1 1.3 grey gyttja clay 10- 15 0.36 6.1 1.2 n 15-20 0.23 8.8 2.4 n 20-25 0.21 10.3 2.7 H 25-30 0.20 10.4 3.0 II 30-35 0.21 10.2 2.8 II 35-40 0.20 10.0 2.7 II

Paijanne 8) Tehinselkä 0- 2 0.082 14.8 3.1 watery sludge 35.2 m 2- 5 0.17 20.1 2.5 soft gyttja 5-10 0.19 10.7 2.5 soft clay 10- 15 0.16 13.5 3.5 n 15- 20 0.17 13.6 3.4 n 20-25 0.18 13.1 3.3 soft clay 25- 30 0.19 11.9 3.2 Tf 30 - 35 0.21 11.1 3.3 tough clay

Päijänne 9) Asikkalansclkäi 0- 2 0.11 10.6 3.0 watery sludge 40.0 m 2- 5 0.19 8.2 1.8 soft gyttja 5-10 0.32 5.6 2.0 soft gyttja clay 10- 15 0.28 7.3 2.1 n 15-20 0.21 10.2 2.9 n 20-25 0.18 12.3 3.3 n 25-30 0.17 12.8 3.6 n 30-35 0.17 11.8 3.4 n

32 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table II. continued

Lake Layer dry wt. Ignition Org. Type volume loss C of sediment Sampling station cm gem"3 % %

Keurusselkä 10) Vuolleselkä 0- 2 0.063 22.5 7.2 black watery mud 16.1 m 2- 5 0.099 20.5 7.2 black mud 5-10 0.16 15.5 4.8 brown mud 10- 15 0.18 14.8 4.9 w 15-20 0.17 15.5 5.2 n 20-25 0.12 22.7 7.0 reddish brown mud 25-30 0.12 23.4 7.5 n

Näsijärvi 11) Näsiselkä 0- 2 0.087 23.3 9.3 watery sulphidic mud 31.0 m 2- 5 0.12 24.8 9.8 sulphidic mud 5-10 0.13 23.3 8.4 sulphidic gyttja 10-15 0.25 10.2 3.4 n 15-20 0.23 10.9 2.8 brown grey clay 20-25 0.22 12.5 3.4 n 25-30 0.17 15.8 4.7 n 30-35 0.19 15.2 4.3 n Näsijärvi 12) Siilinkari 0- 2 0.10 17.7 6.4 reddish brown mud 18.0 m 2- 5 0.19 18.7 7.1 suiphidic mud 5-10 0.23 12.6 4.7 sulphidic gyttja 10- 15 0.23 10.1 2.8 n 15-20 0.22 10.2 3.2 brown grey clay 20-25 0.17 14.0 3.7 •• 25-30 0.17 13.9 3.5 n

Pyhäjärvi 13) Lehtisaari 0- 2 0.13 14.5 5.1 light brown sludge 26.0 m 2- 5 0.23 14.1 5.7 sulphidic sludge gyttja 5-10 0.26 14.4 5.7 sulphidic gyttja 10-14 0.53 9.8 4.6 sulphidic clay

33 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

Table III. Ingnition loss, content of organic carbon, ratio of dry weight to volume and visual description of the sediment samples in 1990.

Lake Layer dry wt Ignition Org. Type Sampling volume loss C of sediment station cm gem-3 % %

Ontojärvi 1) Merjanselkä I. 0- 2 0.082 19.4 6.8 dark mud 12.5 m 2- 5 0.13 18.2 6.7 if Limnos- 5-10 0.21 14.1 5.1 M corer 10- 15 0.17 17.7 6.1 If 15-20 0.16 19.9 6.8 II Ontojärvi 1) Merjanselkä H. 0- 2 0.096 18.9 6.9 watery mud 12.5 m 2- 5 0.18 15.9 5.7 it STUK-corer 5-10 0.23 14.5 4.8 n 10 - 15 0.16 17.9 6.3 it 15-20 0.14 20.4 7.1 dense mud 20-25 0.16 20.4 6.2 ir 25-30 0.37 10.1 3.1 tr Ontojärvi 2) Mulkkusaaret 0- 2 0.037 25.6 8.1 dark mud 25.0 m 2- 5 0.063 25.2 8.3 II 5-10 0.084 23.9 8.3 It 10- 15 0.11 23.7 8.4 II 15-20 0.11 25.7 8.9 II 20- 25 0.10 27.9 9.4 II 25- 30 0.10 29.4 9.8 II Konnevesi 5) Konneselkä 0-2 0.036 27.0 7.4 dark mud 50.0 m 2- 5 0.054 24.5 7.0 n 5-10 0.066 23.0 6.3 n 10- 15 0.085 24.0 7.1 n 15-20 0.091 24.7 7.8 ii 20-25 0.091 26.6 8.1 n 25-30 0.091 27.6 8.6 w

34 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table III. continued

Lake Layer dry wt Ignition Org. Type Sampling volume loss C of sediment station cm gem'3 % %

Päijänne 9) Asikkalanselkä 0- 2 0.079 14.1 3.2 dark mud 41.0 m 2- 5 0.15 10.0 2.2 « 5-10 0.31 5.8 1.5 gyttja 10-15 0.24 19.4 2.1 clay 15-20 0.19 11.6 2.8 clay

Keurusselkä 10) Vuolleselkä 0- 2 0.041 22.3 6.7 mud 15.2 m 2- 5 0.068 23.5 7.2 5-10 0.10 20.0 6.3 10-15 0.17 15.0 4.9 15 -20 0.19 14.4 4.4 20-25 0.18 14.7 4.4 25 -30 0.11 25.2 8.1 Näsijärvi 11) Näsiselkä 0- 2 0.057 22.8 7.8 brown mud 30.0 m 2- 5 0.13 23.6 9.5 sulphidic gyttja 5-10 0.12 24.2 9.2 ti 10- 15 0.21 10.6 2.7 brown gyttja 15-20 0.20 10.9 2.9 brown clay 20-25 0.20 12.3 3.6 ft 25-30 0.16 15.7 4.2 n Pyhäjärvi 13) Lehtisaari 0- 2 0.11 15.5 5.4 brown sludge 27.0m 2- 5 0.21 15.0 5.6 sulphidic gyttja 5-10 0.27 14.7 5.9 sulphidic clay

35 £ Table IV. 1Vertical distribution of gamma--emitting radionuclides in sediment samples in 1988.

Lake Layer Bqkg 1 dry weight Sampling station cm 54Mn «Co 106Ru 11 ^Ag J25Sb 134Cs "7Cs 144Ce

Ontojärvi 1) Merjanselkä 0- 2 0a 0 200 0 23 510 2300 350 12.3 m 2- 5 0 0 0 0 0 77 510 0 2.8.88 5-10 0 0 0 0 0 29 160 0 10- 15 0 0 0 0 0 5.8 39 0 15-20 0 0 0 0 0 0 17 0 20-25 0 0 0 0 0 0 5 0 25-30 0 0 0 0 0 0 0 0

Ontojärvi 2) Mulkkusaaret 0- 2 0 0 0 0 0 80 530 0 24.4 m 2- 5 0 0 0 0 0 25 270 0 2.8.88 5-10 0 0 0 0 0 13 93 0 10- 15 0 0 0 0 0 7.6 41 0 15-20 0 0 0 0 0 0 19 0 20-25 0 0 0 0 0 0 15 0 25-30 0 0 0 0 0 0 0 0

* below detection limit Table IV. continued

Lake Layer Bqkg" 1 dry weight Sampling station cm HMn "Co 106Ru nomAg 125Sb 134Cs 137Cs 144Ce

Pielinen 3) Suurselkä 0- 2 0 0 0 0 0 11 440 0 29.5 m 2- 5 0 0 0 0 0 0 220 0 3.8.88 5-10 0 0 0 0 0 0 8.4 0 10- 15 0 0 0 0 0 0 0 0 20-25 0 0 0 0 0 0 0 0 25-30 0 0 0 0 0 0 0 0 30-35 _b ------

Kallavesi 4) Muuraissaaret 0- 2 0 0 0 0 0 140 630 0 32.2 m 2- 5 0 0 0 0 0 50 410 0 4.8.88 5-10 0 0 0 0 0 6.1 78 0 10- 15 0 0 0 0 0 0 18 0 15-20 0 0 0 0 0 0 5.8 0 20-25 0 0 0 0 0 0 0 0 25-30 0 0 0 0 0 0 0 0 30-35 — - "~ — — — — — w b not measured ^4 00 Table IV. continued

Lake Layer Bq kg"1 dry weight Sampling 106 110m 125 134QJ W, 144, station cm 54M n 60,C o Ru "AAg Sb Cs Ce

[onnevesi 5) Konneselkä 0- 2 0 0 0 0 0 36 160 0 40.0 m 2- 5 0 0 0 0 0 19 94 0 4.8.88 5- 10 0 0 0 0 0 15 66 0 10- 15 0 0 0 0 0 7.1 30 0 15- 20 0 0 0 0 0 5.6 25 0 20- 25 0 0 0 0 0 0 15 0 25 - 30 0 0 0 0 0 0 11 0 30- 35 0 0 0 0 0 0 11 0

äijänne 6) Ristiselkä 0- 2 0 0 76 0 53 1000 3800 0 45.0 m 2- 5 0 0 0 0 0 130 620 0 7.9.88 5- 10 0 0 0 0 0 8.9 160 0 10- 15 0 0 0 0 0 0 11 0 15- 20 0 0 0 0 0 0 0 0 on 20- 25 0 0 0 0 0 0 0 0 25 - 30 0 0 0 0 0 0 0 0 75 0 I 30- 35 0 0 0 0 0 0 0 > to Table IV. continued Lake Layer Bq kg" dry weight i—* Sampling to S4 60 m 137, 144, station cm Mn Co io6Ru nomAg i2sSb Cs Cs Ce

Päijänne 7) Souselkä 0-2 0 0 0 0 o 130 670 o 41.0 m 2-5 0 0 0 0 0 30 210 o 5.8.88 5-10 0 0 0 0 0 3.6 17 o 10- 15 0 0 0 0 0 0 5 o 15 - 20 0 0 0 0 0 0 0 o 20- 25 0 0 0 0 0 0 0 o 25- 30 30- 35 35- 40

Päijänne t/i 8) Tehinselkä 0-2 0 0 0 0 110 2000 7200 0 32.5 m 2-5 0 0 0 0 0 130 570 0 n m 6.9.88 5-10 0 0 0 0 0 29 120 0 JO 10- 15 0 0 0 0 0 0 17 0 m Tl 15- 20 0 0 0 0 0 0 5.8 0 o O 20- 25 0 0 0 0 0 0 0 0 r* 50 25- 30 g? 30- 35 C/J o 2 FINNISH CENTRE FOR RADIAIION AND NUCLEAR SAFETY STUK-A112

U 3 r- o o o o i r- o o o o i i vo

O O O CO O 1 1 1 i i O © i/"> i-i Ö CO r* r-l Q0«8S§SH ° O ** (oN 1-4

O O Ov O O I I I © <* © O I I ö O rr CO 8 (S .-H •ä vO rl n co zo CO X5 >•. C/3 O O O O I I I o o o o o i i "O 8 12 5 CO 00 i 00 M on O* < 00 O O O O I O O O O O I I

3 O O O O O I I I O O O O O I I Oi o ci Cl Cl

o u VO O O O O I I O O O O O I I s

c O O O O O I O O O O O I I

ci »O o m o in o in r i u~> o m o »n o r—i t-t rl rl cO ro H H N M rt 11 l 1 • i i i i l o 1 1 i i i i i 1 I I I I I I I S O i/1 O uo o 2 e T-H ^ ri n CO r-i n-* ri n

A! anselk ä « J 6 §8 40. 0 m 6.9.8 8 Asikka l 9

mplin g i e itiö n :« /«•"S «5 #5 t? Ov 2 Päi i 2

40 Table IV. continued H C 71 i > Lake Layer Bq kg" dry weight to Sampling 54 60, 106 nOmAg 125Sb 134^ 137, 144, station cm Mn Co Ru Cs Ce

Näsijärvi 11) Näsiselkä 0-2 9.9 16 1100 83 990 15600 55700 930 31.0 m 2-5 0 0 0 0 40 860 3300 35 8.9.88 5-10 0 0 0 0 0 110 610 0 10- 15 0 0 0 0 0 28 130 0 15- 20 0 0 0 0 0 7.0 27 0 20- 25 0 0 0 0 0 0 9.3 0 25 - 30 0 0 0 0 0 0 4.9 0 30- 35 0 0 0 0 0 0 8.1 0 •n

V5 Näsijärvi X 12) Siilinkari 0-2 0 0 640 50 440 11400 41000 540 n 18.0 m 2-5 0 0 0 0 49 950 3600 46 m 73 8.9.88 5-10 0 0 0 0 0 59 320 0 m ti 10- 15 0 0 0 0 0 14 61 0 n o 15- 20 0 0 0 0 0 2.4 14 0 jo 20- 25 0 0 0 0 0 3.1 12 0 73 > 25 - 30 0 0 0 0 0 0 9.9 0 i3i to Table IV. continued £ 3

C/5 X o w 3 Lake Layer Bq kg"1 dry weight > Sampling »jg f3n station cm 54Mn wCo 106Ru UOraAg 12SSb 134Cs "7Cs 144Ce § 3 • ?3 -4

Pyhäjärvi 13) Lehtisaari 0-2 0 0 630 53 410 9500 34000 420 o 26.0 m 2-5 0 0 190 0 130 2700 9500 170 z 9.9.88 5-10 0 0 0 0 0 110 510 0 10-15 0 0 0 0 0 0 130 0

C/3

i > i—i to FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table V. Vertical distribution of gamma-emmitting radionuclides in sediment samples in 1990.

Lake Bq kg"1 dr>' weight Sampling Layer station cm »Co I06Ru 125Sb 134Cs 137Cs 144Ce

Ontojärvi 1) Merjanselkä I 0 - 2 01 450 0 250 2100 69 12.5 m 2 - 5 0 0 0 250 2200 0 21.8.90 5 - 10 0 0 0 25 290 0 (Limnos-corer) 10 - 15 0 0 0 0 39 0 15 - 20 0 0 0 0 7 0

Ontojärvi 1) Merjanselkä II 0 - 2 0 0 0 270 2200 120 12.5 m 2 - 5 0 0 0 140 1300 0 21.8.90 5 - 10 0 0 0 14 170 0 (STUK-corer) 10 - 15 0 0 0 0 50 0 15 - 20 0 0 0 0 19 0 20 - 25 0 0 0 0 0 0 25 - 30 0 0 0 0 0 0

Ontojärvi 2) Mulkkusaaret 0 - 2 0 0 35 270 2100 120 25.0 m 2 - 5 0 200 120 390 3000 150 21.8.90 5 - 10 0 0 0 120 1200 0 10 - 15 0 0 0 0 210 0 15 - 20 0 0 0 0 39 0 20 - 25 0 0 0 0 13 0 25 - 30 0 0 0 0 5.9 0

Konnevesi 5) Konneselkä 0 - 2 0 0 350 5000 32600 0 50.0 m 2 - 5 0 0 100 1600 11000 0 22.8.90 5 - 10 0 0 0 71 790 0 10 - 15 0 0 0 17 160 0 15 - 20 0 0 0 0 41 0 20 - 25 0 0 0 0 3.8 0 25 - 30 0 0 0 0 0 0

' below detection limit

43 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

Table V. continued

Lake Bq kg"1 dry weight Sampling Layer station cm "Co 106Ru 125Sb 134Cs 137Cs ,44Ce

Päijänne 9) Asikkalanelkä 0 - 2 0 0 330 6900 43800 0 41.0 m 2 - 5 0 0 39 670 4900 0 24.8.90 5 - 10 0 0 0 9.4 87 0 10 - 15 0 0 0 0 21 0 15 - 20 0 0 0 0 0 0

Keurusselkä 10) Vuolleselkä 0 - 2 0 0 180 2300 15400 0 15.2 m 2 - 5 0 0 560 5700 37200 0 3.8.90 5 - 10 0 0 82 1100 7200 0 10 - 15 0 0 0 35 240 0 15 - 20 0 0 0 0 6.3 0 20 - 25 0 0 0 0 0 0 25 - 30 0 0 0 0 0 0

Näsijärvi 11) Näsiselkä 0 - 2 11 280 400 7400 48600 150 30.0 m 2 - 5 0 0 140 1900 12500 0 23.8.90 5 - 10 0 0 0 81 710 0 10 - 15 0 0 0 6.3 76 0 15 - 20 0 0 0 0 5 0 20 - 25 0 0 0 0 2 0 25 - 30 0 0 0 0 2 0

Pyhäjärvi 13) Lehtisaari 0 - 2 0 0 98 3100 19800 0 27.0 m 2 - 5 0 0 180 3800 25300 0 23.8.90 5 - 10 0 0 38 560 3800 0

44 FINNISH CFNTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

Table 11. The total amounts of 137Cs in bottom sediments (Bq m~2) in 1969, 1978, 1988 and 1990 and the total deposition on October 1, 1987.1

Bq m-2 m Lake Total Sampling station 1969 1978 1988 1990 Deposition 1.10.87

Ontojärvi 1) Merjanselkä 2500 2800 10000 14000 6000-11000 2) Mulkkusaaret _» 2000 2300 14000 6000-11000

Pielinen 3) Suurselkä - - 2800 - 0- 6000

Kallavesi 4) Muuraissaaret - - 3700 - 11000-23000

Konnevesi 5) Konneselkä - - 1100 45000 23000 - 45000

Päijänne 6) Ristiselkä 2200 2100 12000 - 11000-23000 7) Souselkä 1400 2100 3700 - 23000 - 45000 8) Tehinselkä - 1600 16000 - 45000 - 78000 9) Asikkalanselkä 1700 1000 50000 92000 45000 - 78000

Keurusselkä 10) Vuolleselkä - - 19000 130000 45000 - 78000

Näsijärvi 11) Näsiselkä 1600 4200 110000 110000 45000 - 78000 12) Siilikari - 2700 110000 - 45000 - 78000

Pyhäjärvi 13) Lehtisaari 10000 13000 160000 250000 45000 - 78000

a no sampling

45 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

PUBLICATIONS BY THE FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY (STUK)

STUK-A reports:

STUK-A108 Arvela H, Mäkeläinen I, Castren STUK-A98 Kosunen A, Järvinen H, Vatnitskij O. Otantatutkimus asuntojen radonista S, Ennakov I, Chervjakov A, Kulmala J, Suomessa. Helsinki, 1993. Pitkänen M, Väyrynen T. Väänänen A. Intercomparison of radiotherapy treatment STUK-A105 Mustonen R. Building materials planning systems usirg calculated and measured as sources of indoor exposure to ionizing dose distributions for external photon and radiation. Helsinki, 1992. electron beams. Helsinki, 1991.

STUK-A104 Toivonen H, Klemola S, Lahtinen STUK-A97 Levai F, Tikkinen J, Tarvainen M, J, Leppänen A, Pöllänen R, Kansanaho A, Arit R. Feasibility studies of computed Savolainen A.L., Sarkanen A, Valkama I, Jäntti tomography in partial defect detection of spent M. Radioactive Release from Sosnovyy Bor, St BWR fuel. Helsinki, 1990. Petersburg, in March 1992. Helsinki, 1992. STUK-A93 Puhakainen M, Rahola T. STUK-A103 Uus E, Sjöblom K-L, Radioactivity of sludge in Finland in 1988- Ikäheimonen T.K, Saxen R, Klemola S. 1990. Supplement 5 to Annual Report STUK- Monitoring of radionuclides in the Baltic Sea in A89. Helsinki, 1991. 1989-1990. Helsinki, 1993. STUK-A92 Klemola S, »us E, Sjöblom K-L, STUK-A102 «us E, Sjöblom K-L, Klemola S, Arvela H, Blomqvist L. Monitoring of Arvela H. Monitoring of radionuclides in the radionuclides in the environs of the Finnish environs of Finnish nuclear power plants in nuclear power stations in 1988. Supplement 3 to 1989-1990. Helsinki, 1992. Annual Report STUK-A89. Helsinki, 1991.

STUK-A101 Toivonen M. Improved processes STUK-A91 Rahola T, Suomela M, Hiukka E, in therapy dosimetry with solid LiF Pusa S. Radioactivity of people in Finland in thermoluminescent detectors. Helsinki, 1991. 1988. Supplement 2 to Annual Report STUK- A89. Helsinki, 1991. STUK-AlOOServomaa K Biological effects of radiation: The induction of malignant STUK-A99 Saxen R, Ikäheimonen T.K, Uus E. transformation and programmed cell death. Monitoring of radionuclides in the Baltic Sea in Helsinki, 1991. 1988, Supplement 1 to Annual Report STUK- A89. Helsinki 1990. STUK-A99 Ruosteenoja E. Indoor radon and risk of lung cancer: an epidemiological study in Finland. Helsinki, 1991.

1 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

STUK-A88 Valtonen K. BWR stability STTJK-A78 Rantavaara A. Radioactivity of analysis. Helsinki, 1990. foodstuffs in Finland in 1987-88. Supplement 4 to Annual Reports STUK-A74 and STUK-A89. STUK-A87 Servomaa A, Rannikko S, Nikitin Helsinki, 1991. V, Golikov V, Ermakov I, Masarskyi L and Saltukova L. A topographically anatomically STUK-A77 Saxen R, Rantavaara A. unified phantom model for organ dose Radioactivity of surface water and fresh water determination in radiation hygiene. Helsinki, fish in Finland in 1987. Supplement 3 to Annual 1989. Report STUK-A74. Helsinki, 1990.

STUK-A86 Aro I. Studies on severe accidents STUK-A76 Arvela H, Markkanen M, Lemmelä in Finnish nuclear power plants. Helsinki, 1989. H, Blomqvist L Environmental gamma radiation and fallout measurements in Finland, STUK-A85 Hoikkala M, Lappalainen J, 1986-87. Supplement 2 to Annual Report Leszczynki K, Paile W. Väestön altistuminen STUK-A74. Helsinki, 1989. ultraviolettisäteilylle Suomessa ja säteilymittaukset. Helsinki, 1990. STUK-A75 Saxin R, Aaltonen H, Ikäheimonen TK. Airborne and deposited radioactivity in STUK-A84 Puhakainen M, Rahola T. Finland in 1987. Supplement 1 to Annual Radioactivity of sludge in Finland in 1987. Report STUK-A74. Helsinki, 1990. Supplement 10 to Annual Report STUK-A74. Helsinki, 1989. STUK-A74 Suomela M, Blomqvist L, Rahola T and Rantavaara A. Studies on environmental STUK-A83 Uus E, Klemola S, Sjöblom K-L, radioactivity in Finland in 1987. Annual Report. Ikäheimonen TK. Radioactivity of along the Helsinki, 1991. finnish coast in 1987. Supplement 9 to Annual Report STUK-A74. Helsinki, 1988. STUK-A73 Järvinen H, Bregazde JI, Berlyand VA, Toivonen M. Comparison of The National STUK-A82 Ikäheimonen TK, Uus E, Saxen R. Standards for the measurements of absorbed Finnish Studies in radioactivity in the Baltic Sea dose at "Co gamma radiation. Helsinki, 1988. in 1987. Supplement 8 to Annual Report STUK-A74. Helsinki, 1988. STUK-A72 Keskitalo J. Effects of thermal discharges on the benthic vegetation and STUK-A81 Rahola T, Suomela M, Hiukka E, outside the Olkiluoto nuclear Pusa S. Radioactivity of people in Finland in power station, west coast of Finland: summary. 1987. Supplement 7 to Annual Report STUK- Helsinki, 1988. A74. Helsinki, 1989. STUK-A71 Keskitalo J. Effects of thermal STUK-A80 Rissanen K, Rahola T, Hiukka E, discharges on the benthic vegetation and Alftan A. Radioactivity in reindeer, game, fish phytoplankton outside the Olkiluoto nuclear and plants in finnish Lappland in 1987. power station, west coast of Finland. Helsinki, Supplement 6 to Annual Report STUK-A74. (to 1988. be published in 1991) STUK-A76 Hellmuth K-H. Rapid STUK-A79 Sjöblom K-L, Klemola S, Uus E, determination of strontium-89 and strontium-90 Arvela H, Blomqvist L. Monitoring of -experiences and results with various methods radioactivity in the environs of finnish nuclear after the Chernobyl accident in 1986. Helsinki, power stations in 1987. Supplement 5 to annual 1987. Report STUK-A74. Helsinki, 1989.

•7 FINNISH CENTRE FOR RADIATION STUK-A112 AND NUCLEAR SAFETY

STUK-A69 Salmenhaara S, Tarvainen M. STUK-A61 Saxen R, Rantavaara A. Nondestructive measurements with a WWER- Radioactivity of fresh water fish in Finland after 440 fuel assembly model using neutron and the Chernobyl accident in 1986. Supplement 6 gamma sources. Helsinki, 1987. to Annual Report STUK-A55. Helsinki, 1987.

STUK-A68 Puhakainen M, Rahola T, Suomela STUK-A60 Saxtn R, Aaltonen H. M. Radioactivity of sludge after the Chernobyl Radioactivity of surface water in Finland after accident in 1986. Supplement 13 to Annual the Chernobyl accident in 1986. Supplement 5 Report STUK-A55. Helsinki, 1987. to Annual Report STUK-A55. Helsinki, 1987.

STUK-A67 Ilus E, Sjöblom K-L, Aaltonen H, STUK-A5* RanUvaara A. Radioactivity of Klemola S, Arvela H. Monitoring of vegetables and mushrooms in Finland after the radioactivity in the environs of Finnish nuclear Chernobyl accident in 1986. Supplement 4 to power stations in 1986. Supplement 12 to Annual Report STUK-A55. Helsinki, 1987. Annual Report STUK-A55. Helsinki, 1987. STUK-A58 RanUvaara A, Haukka S. STUK-A66 Uus E, Sjöblom K-L, Saxen R, Radioactivity of milk, meat, cereals and other Aaltonen H, Taipale TK. Finnish studies on agricultural products in Finland after the radioactivity in the Baltic Sea after the Chernobyl accident in 1986. Supplement 3 to Chernobyl accident in 1986. Supplement 11 to Annual Report STUK-A55. Helsinki, 1987. Annual Report STUK-A55. Helsinki, 1987. STUK-A57 Saxen R, Taipale TK, Aaltonen H. STUK-A65 Arvela H, Blomqvist L, Lemmelä Radioactivity of wet and dry deposition and soil H, Savolainen A-L, Sarkkula S. Environmental in Finland after the Chernobyl accident in 1986. gamma radiation measurements in Finland and Supplement 2 to Annual Report STUK-A55. the influence of the meteorological conditions Helsinki, 1987. after the Chernobyl accident in 1986. Supplement 10 to Annual Report STUK-A55. STUK-A56 Sinkko K, Aaltonen H, Taipale TK, Helsinki, 1987. Juutilainen J. Airborne radioactivity in Finland after the Chernobyl accident in 1986. STUK-A64 Rahola T, Suomela M, niukka E, Supplement 1 to Annual Report STUK-A55. Puhakainen M, Pusa S. Radioactivity of people Helsinki, 1987. in Finland after the Chernobyl accident in 1986. Supplement 9 to Annual Report STUK-A55. STUK-A55 Studies on environmental Helsinki, 1987. radioactivity in Finland in 1986. Annual Report. Helsinki, 1987. STCK-A63 Rissanen K, Rahola T, Hiukka E, Alfthan A. Radioactivity of reindeer, game and STUK-A54 Studies on environmental fish in Finnish Lapland after the Chernobyl radioactivity in Finland 1984-1985. Annual accident in 1986. Supplement 8 to Annual Report. Helsinki, 1987. Report STUK-A55. Helsinki, 1987. STUK-A53 Järvinen H, Rantanen E, Jokela STUK-A62 Rantavaara A, Nygren T, Nygrin K. Testing of radiotherapy dosimeters in K, Hyvönen T. Radioactivity of game meat in accordance with IEC specification. Helsinki, Finland after the Chernobyl accident in 1986. 1986. Supplement 7 to Annual Report STUK-A55. Helsinki, 1987. STUK-A52 af Ekenstam G, Tarvainen M. Independent bumup verification of BWR-type nuclear fuel by means of the WC& activity. Helsinki, 1987.

3 FINNISH CENTRE FOR RADIATION AND NUCLEAR SAFETY STUK-A112

STUK-A51 Arvela H, Winqvist K. Influence cf source type and air exchange on variations of indoor radon concentration. Helsinki, 1986.

STUK-A50 Järvinen H, Rannikko S, Servomaa A. Report on the Nordic-Soviet meeting on standard and applied dosimetry, Helsinki, 9-11 November 1983. Helsinki, 1984.

STUK-A49 Tarvainen M, Riihonen M. Spent fuel measurements at Loviisa nuclear power station. May, 1982. Helsinki, 1984.

The full list of publications is available from:

Library Finnish Centre for Radiation and Nuclear Safety P.O. BOX 268 SF-00101 HELSINKI Finland

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